I didn't know citrus black fly can cause a lot of damage, sucking up as much as 80% of trees yield capacity. You can read more about it:

http://uk.reuters.com/article/environmentNews/idUKN2434864420080325

Without the parasites to control it, it can be devastating. When it entered Florida in 1976, there were those prophets of doom and gloom who said it was the end of our industry (we've heard that one many times). Trees were completely defoliated, and some died.

But several parasites were brought in from Mexico, and one of them turned out to like Florida's climate. Since then, CBF has been a very minor pest on citrus, never warranting spraying or other control measures. I rather enjoy finding it now -- it's the "find of the day" if you're taking a class on a scouting walk.

Most of Sao Paulo's citrus region is quite similar, climatologically, to this part of Florida, so I suspect that all they need to do is introduce the parasite.